Obesity is a difficult to treat chronic condition defined by a body mass index (BMI=mass/height2[kg/m]) greater than 30. For obese persons, excessive weight is commonly associated with increased risk of cardiovascular disease, diabetes, degenerative arthritis, endocrine and pulmonary abnormalities, gallbladder disease and hypertension. Additionally, such persons are highly likely to experience psychological difficulties because of lifestyle restrictions such as reduced mobility and physical capacity, due to back pain joint problems, and shortness of breath. In severe cases, this can contribute to absenteeism and unemployment. Moreover, impairment of body image can lead to significant psychological disturbances. Repeated failures of dieting and exercise to resolve the problem of obesity can result in feelings of despair and the development of clinical depression.
U.S. Pat. No. 6,600,953 to Flesler et al., which is assigned to the assignee of the present patent application and is incorporated herein by reference, describes apparatus for treating a condition such as obesity. The apparatus includes a set of one or more electrodes, which are adapted to be applied to one or more respective sites in a vicinity of a body of a stomach of a patient. A control unit is adapted to drive the electrode set to apply to the body of the stomach a signal, configured such that application thereof increases a level of contraction of muscle tissue of the body of the stomach, and decreases a cross-sectional area of a portion of the body of the stomach for a substantially continuous period greater than about 3 seconds.
U.S. Pat. No. 6,571,127 and PCT Patent Publication WO 99/03533 to Ben-Haim et a., which are incorporated herein by reference, describe apparatus and methods for applying signals to smooth muscle so as to modify the behavior thereof. In particular, apparatus for controlling the stomach is described in which a controller applies an electrical field to, electrodes on the stomach wall so as to modify the reaction of muscle tissue therein to an activation signal, while not generating a propagating action potential in the tissue. In the context of the present patent application and in the claims, the use of such a non-excitatory signal to modify the response of one or more cells to electrical activation thereof without inducing action potentials in the cells, is referred to as Excitable-Tissue Control (ETC). Use of an ETC signal is described with respect to treating obesity, by applying the ETC signal to the stomach so as to delay or prevent emptying of the stomach. In addition, a method is described for increasing the motility of the gastrointestinal tract, by applying an ETC signal to a portion of the tact in order to increase the contraction force generated in the portion and the stretching of nearby tissue.
U.S. Patent Application Publication 2004/0147816 to Policker et al., which is assigned to the assignee of the present patent application and is incorporated herein by reference, describes diet evaluation gastric apparatus, which detects when a patient swallows, and detects the type and amount of matter ingested. The apparatus includes electrodes adapted to be coupled to the fundus and antrum of the patient and to measure electrical and mechanical activity therein, and a control unit to analyze such electrical and mechanical activity and optionally apply electrical energy to modify the activity of tissue of the patient.
In an article by Tougas et al., entitled, “Assessment of gastric emptying using a low fat meal: Establishment of international control values, ” American Journal of Gastroenterology, 95(6), 2000, pp. 1456-1462, which is incorporated herein by reference, a study is described in which a simplified scintigraphic measurement of gastric emptying was compared to coventional gastric scintigraphic techniques and normal gastric emptying values defined in healthy subjects.
An article by Choli et at., entitled, “[13C] Octanoic acid breath test for gastric emptying of solids: Accuracy, reproducibility, and comparison with scintigraphy,” Gastroenterology, 112, 1997, pp. 1155-1162, which is incorporated herein by reference, describes a breath test using 13C to measure gastric emptying of solids.
An article by English et at., entitled, “Food fails to suppress ghrelin levels in obese humans, ” J Clin Endocrinol Metab, June 2002, 87(6): 2984-2987, which is incorporated herein by reference, describes ghrelin as the first circulating hormone shown to stimulate feeding in humans following systemic administration. Food consumption was known to decrease circulating ghrelin concentrations in lean subjects. The authors investigated the effects of a test meal on plasma ghrelin and leptin cocentrations in 13 lean and 10 obese subjects. Fasting ghrelin was significantly higher in lean than in obese subjects, and fell by 39.5% thirty minutes after eating in the lean group before returning rapidly towards baseline values. There was no change in circulating, ghrelin in the obese group. Circulating leptin concentration also fell acutely 15 minutes following food intake in lean but not obese subjects. The authors concluded that (a) obese subjects do not exhibit the decline in plasma ghrelin and leptin seen after a meal in the lean, and (b) the role of the decline in leptin is unclear but given the orexigenic properties of ghrelin, the lack of suppression following a meal in obese subjects could lead to increased food consumption and suggests that ghrelin may be involved in the patlhophysiology of obesity.